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George E. Carvell, PhD, PT   University of Pittsburgh
 
LOCAL POTENTIALS I: SYNAPTIC POTENTIALS- NEUROMUSCULAR JUNCTION
BC&P Fig 5.7  p. 106
  The Neuromuscular Junction (NMJ) is a special excitatory synapse. Unlike most excitatory synapses in the CNS, the connection between an Alpha Motor Neuron in the spinal cord and the target muscle fibers in the periphery provides a ‘guaranteed’ transmission of a signal to move. A Nerve Action Potential (NAP) produces a Muscle Action Potential (MAP) by action of a chemical messenger passed between the nerve and muscle. Under normal physiological conditions, the MAP always results in a contraction of the innervated, unfatigued muscle fibers (motor unit contraction). The chemical messenger at the NMJ is Acetylcholine (ACh). Ach is stored in synaptic vesicles in the axon terminal. An NAP causes the vesicles to bind to the axon terminal and release Ach into the synaptic cleft. ACh receptors localized to the NMJ on the muscle membrane bind the neurotransmitter. This chemically-gated process opens ion channels to allow Na+ and K+ ions to pass through the ion pore. This results in a large depolarization that triggers the MAP.
PLEASE CONTINUE
SYNAPSES PROVIDE CHEMICALLY-GATED CONNECTIVITY BETWEEN EXCITABLE CELLS (SYNAPTIC POTENTIALS)
PLAY THE MOVIE
Movie shows activation of an Alpha Motor Neuron, initiating an AP that travel down the Alpha Motor Axon to three ‘representative’ muscle fibers of the motor unit. Muscle fibers contract after a Muscle Action Potential discharges due to synaptic depolarization of each muscle fiber at the motor end-plate region (NMJ).
GMOMM
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